1. Field of the Invention.
This invention is generally concerned with stabilizing the catalytic activity of those zeolite catalysts employed in (1) fluid catalytic cracking, reforming, etc. processes used in the petroleum industry (as well as in various chemical manufacturing processes that do not involve petroleum products), (2) fixed bed catalytic processes (involving petroleum products or non-petroleum products), (3) fluid bed catalytic processes (involving petroleum products or non-petroleum products) or (4) so-called deep catalytic cracking ("DCC") (involving petroleum or non-petroleum products). Such zeolite "stabilization" implies a reduction in the rate at which a given zeolite's catalytic activity is lost due to such factors as thermally induced damage to that zeolite's molecular structure, as well as accumulation of coke, sulfur and/or undesired metals on its catalytically active sites. More particularly, this invention is concerned with stabilizing zeolites against these harmful effects by chemically reacting them with clay materials (rather than merely physically mixing them with such materials) through the use of certain alkaline, phosphate-containing compounds, certain pH conditions and certain reaction time parameters.
2. Nature of Zeolites.
As used in this patent disclosure, the term "zeolite" should be taken to include any crystalline silicate having a zeolite crystalline structure. Detailed descriptions of such crystalline structures may be found in D. W. Breck, Zeolite Molecular Sieves, John Wiley and Sons, New York, 1974, see also: Society of Chemical Engineering (London), Monograph Molecular Sieves, p. 186 (1968) by C. V. McDaniel and P. K. Maher; both of these reference works are incorporated herein by reference. Hydrothermally and/or chemically modified versions of various zeolites, such as the so-called "ultrastable" zeolites (e.g., those described, in U.S. Pat. No. 3,293,192 and U.S. Pat. No. 3,506,400), also should be regarded as being zeolites for the purposes of this patent disclosure.
Most zeolites have particles sizes ranging from about 2 to about 10 microns and, hence, are too small for direct use as catalysts such as (FCC) particles (which are usually sized at about 60-80 microns). Consequently, almost all zeolitic crystalline alumino silicates that are used as catalysts are physically "embedded" in a matrix or binder material in order to make composite zeolite/binder particles having more appropriate sizes. Typically, the major component(s) of those matrix or binder materials used to make zeolite-containing catalysts are: silica, alumina, magnesia, zirconia, boria, aluminum chlorohydrol and various non-ionic clays. Alumina, silica and silica alumina are the more preferred materials since they generally serve to impart toughness and attrition-resistant qualities to zeolite/binder catalyst materials.
Kaolin, montmorillinite and bentonite are the most widely used non-ionic clay binder materials (see for example U.S. Pat. Nos. 3,252,757, 3,252,889 and 3,743,594). They are used primarily because they are far less expensive than the alumina, silica, etc. compounds they may replace in zeolite/binder systems. Such non-ionic clays must, however, be used sparingly. That is to say that most high non-ionic clay content catalyst particles (e.g., those containing more than about 20 weight percent clay) usually lack the quality of "toughness" or "attrition-resistance." This lack of toughness or attrition resistance eventually leads to the creation of smaller catalyst particles. This, in turn, leads to unacceptable elutriation losses of these very expensive materials.
Various methods of physically incorporating zeolite particles into clay-containing binder materials are described in the patent literature. For example, U.S. Pat. Nos. 3,609,103; 3,676,330; 3,835,031; 4,240,899; 4,740,292; 4,898,846; 4,911,823; 5,102,530; 5,219,536 and 5,270,272 teach various methods of incorporating zeolite(s) particles into clay-containing binder systems. The zeolite particle components of the resulting zeolite/clay catalysts are usually discrete units--i.e., the zeolite particles are physically embedded in an otherwise continuous phase of the binder material. The prior art also has recognized that certain different zeolites can be used in combination to produce synergistic effects. For example, International Application Number PCT/US94/07865 teaches use of catalysts comprised of zeolite beta and a shape selective cracking catalyst such as ZSM-5 (as well as other catalyst such as zeolite Y). These zeolite blends can be used in the form of composite particles or as separate and distinct ZSM-5 particles and zeolite beta particles --all of which are made through use of some appropriate matrix-forming material. With respect to such matrix materials this PCT patent application states that:
It may be desirable to incorporate the zeolites (any of them, ranging from the conventional zeolite Y to zeolite beta or ZSM-5) into a conventional matrix.
Such matrix materials include synthetic and naturally occurring substances, such as inorganic materials, e.g., clay, silica, and metal oxides such as alumina, silica-alumina, silica-magnesia, etc. The matrix may be in the form of a cogel or sol . . . The matrix material may include phosphorus that is derived from a water soluble phosphorus compound including phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium hypophosphate, ammonium phosphite, ammonium hypophosphite and ammonium dihydrogen orthophosphite.
3. Description of Prior Art Re: Use of Phosphate Treated Clays.
Phosphate treated clays have been used in various zeolite/binder catalyst systems. By way of example, U.S. Pat. Nos. 5,190,902 ("the '902 patent") and 5,288,739 ("the '739 patent") teach that attrition-resistant binder materials for a variety of catalysts (including zeolites) can be prepared by a process wherein a slurry of clay particles is brought to either a low pH level (e.g., 1.0 to 3.0) or to a high pH level (e.g., 14.0 to 10.0) and mixed with a phosphate-containing compound. The resulting slurry is then spray dried and the particulate products calcined to produce attrition-resistant particles. For reasons that will be made more apparent in later portions of this patent disclosure, these two patents are particularly relevant to the teachings of the present patent disclosure and, hence, they are each incorporated herein by reference.
U.S. Pat. No. 5,521,133 teaches production of catalysts by a process wherein phosphoric acid is injected in a neutral to mildly alkaline kaolin slurry immediately prior to spray drying. This is done in order to improve the attrition resistance properties of the resulting catalysts. U.S. Pat. Nos. 5,231,064 and 5,348,643 teach processes for converting feedstock hydrocarbon compounds through use of zeolite/clay catalysts whose ingredients have been treated with a phosphorus-containing compound, for example, ammonium dihydrogen phosphate or phosphoric acid, and wherein the zeolite/clay slurry used to make these catalysts is spray dried at a low pH, e.g., preferably at a pH lower than 3. This process also is characterized by its relatively short aging times (e.g., less than 30 minutes). U.S. Pat. No. 3,932,268 teaches a catalyst composition comprising an ion-exchanged synthetic crystalline faujasite and an amorphous alumina-silica residue of a caustic leached calcined kaolin clay which has undergone a kaolin exotherm reaction during a preceding calcination procedure. U.S. Pat. No. 4,235,753 discloses crystalline zeolitic aluminosilicate catalysts made from calcined kaolin clay that has been treated with an aqueous alkaline liquid. U.S. Pat. No. 5,312,792 teaches a method for preparing a phosphorous-containing ultrastable Y-zeolite which comprises (a) ion-exchanging and washing sodium Y zeolite with an ammonium salt solution and water to obtain a Y-zeolite, (b) combining the washed Y-zeolite with an aqueous solution of a phosphorus compound selected from the group consisting of H.sub.3 PO.sub.4, NH.sub.4 H.sub.2 PO.sub.4, (NH.sub.4).sub.2 HPO.sub.4, and Na H.sub.2 PO.sub.4 to obtain a Y-zeolite that contains about 0.1 to 5 weight percent P.sub.2 O.sub.5, (c) heating the phosphorus-containing Y-zeolite of step (b) in the presence of steam to obtain a phosphorus-containing ultrastable Y-zeolite and (d) washing the phosphorus-containing ultrastable Y-zeolite to remove sodium ions.